a. Field of the Invention
The present invention generally pertains to fluid dispensing systems and more particularly to actuators that control the amount of a fluid being dispensed.
b. Description of the Background
Fluid dispensers are used in different manufacturing industries to dispense fluids, such as an adhesive, plastisol, sealant or other compounds. In the container industry, for example, it is common to apply a sealant to a can end prior to assembly. The sealant provides a proper seal between the end and a body of a can.
In a typical actuator, a valve is simply opened and closed to dispense a fluid. Existing electrically-controlled valves typically contain two parts: an actuator that quickly opens and closes the valve, and an adjustable stop that sets how far the valve is opened when it is actuated. The actuator that opens and closes the valve may be a solenoid, pneumatic cylinder, or other device designed to quickly open and close the valve. The adjustable stop may be moved by a stepper motor, a stepper solenoid, or by a manual adjustment. One system is described in U.S. Pat. No. 6,010,740 of Rutledge et al. entitled “Fluid Dispensing System,” which is specifically incorporated herein by reference for all that it discloses and teaches.
Using a solenoid to quickly open and close a valve presents some limitations. The mechanism is designed to open and close the valve as quickly as possible. Yet the mechanism has a response time that delays the opening and closing of the valve. The response time may vary due to such factors as the length of stroke. Further, the response of the valve may change with the temperature of the actuator. As the actuator heats up due to repetitive use or environmental factors, the force applied by the actuator may change, thereby changing the response of the valve. The valve itself has a rate of opening and closing that cannot be controlled. Additionally, the exact position of the valve is typically unknown during movement, increasing variability.
A second limitation is that there is typically no way to vary the flow rate of the liquid at any point during the period that the valve is being actuated. In some applications, such as the application of sealant during the manufacturing of cans, it may be desirable to add more sealant in one area and less in another.